The invention concerns a method for preparing a weft thread on weaving machines, i.e. a method for presenting weft threads of a particular length intermittently to a thread insertion mechanism, so that on each weaving cycle a particular length of weft thread is inserted into the shed of the weaving machine. The invention also concerns a weaving machine equipped to use this method.
A known method of providing a particular length of weft thread on each weaving cycle is to wind weft threads during a prewinder, and at each insertion to release a certain number of windings from said prewinder, as known from amongst other U.S. Pat. No. 4,673,004 of the present applicant.
Such prewinders however have the disadvantage that the force necessary to draw the weft thread from the prewinder drum is relatively high, so that there is a high tension on the thread during its insertion into the shed, and also the disadvantage that the thread is braked during its insertion into the shed, so that the speed with which the thread is inserted into the shed is limited.
Another known of providing weft threads is to use a weft accumulator in which the weft thread is laid against a wall. An example is a thread accumulator in which the weft thread is laid spirally against the inside wall of a tube by means of a blower nozzle, after which lengths of weft thread can be drawn intermittently from said tube. The adjustment for releasing exactly one length of weft thread each time is obtained by means of e.g. a thread clip and suitably-controlled thread feed rollers, such that, as known from Dutch patent application No. 86.02741 of the present applicant, which corresponds to U.S. Pat. No. 4,821,781, the correct length of thread is released by the thread feed rollers at the moment the thread clip is closed.
Although such a weft accumulator mechanism has the advantage that the resistance that has to be overcome in order to draw the weft thread from the tube is very low, it has the disadvantage that very precise control of the above-mentioned thread feed rollers and thread clip are necessary in order to release exactly one length of weft thread.